The present invention relates generally to suspended semiconductor device structures and in particular to disposing different device types on the same substrate.
Field effect transistors (FETs) can be semiconductor devices fabricated on a bulk semiconductor substrate or on a silicon-on-insulator (SOI) substrate. FET devices generally consist of a source, a drain, a gate, and a channel between the source and drain. The gate is separated from the channel by a thin insulating layer, typically of silicon oxide, called the gate oxide. A voltage drop generated by the gate across the oxide layer induces a conducting channel between the source and drain thereby controlling the current flow between the source and the drain. Current integrated circuit designs use complementary metal-oxide-semiconductor (CMOS) technology that use complementary and symmetrical pairs of p-type and n-type metal oxide semiconductor field effect transistors (MOSFETs) for logic functions.
The integrated circuit industry is continually reducing the size of the devices, increasing the number of circuits that can be produced on a given substrate or chip. It is also desirable to increase the performance of these circuits, increase the speed, and reduce the power consumption. A three-dimensional chip fabrication approach, such as a finFET, has been developed for semiconductor devices. A finFET is a non-planar FET, generally regarded as a type of suspended channel device. The “fin” is a narrow, vertical silicon base channel between the source and the drain. The fin is covered by the thin gate oxide and bordered on two or three sides by an overlying gate structure. The multiple surfaces of the gate allow for more effective suppression of “off-state” leakage current. The multiple surfaces of the gate also allow enhanced current in the “on” state, also known as drive current. These advantages translate to lower power consumption and enhanced device performance.
In the area of suspended channel device structures, the suspension step is a pivotal point in the process sequence. In several integration flows, the use of an SOI wafer is often proposed, however, this adds to the overall technology cost, so the use of a bulk silicon wafer is often preferred. Several flows for bulk wafers have been considered, but these process flows may often rely on oxidizing a region under the fin or nanowire after the channel is protected by a hard mask and spacer, resulting in volumetric expansion of the oxide underneath the channel.